The proposed research represents a continuation of studies on some of the basic physiological, morphological, and pharmacological properties of mammalian glia and neurons in in vitro systems. This research will also investigate the characteristics and homeostatic regulation of ionic and volume fluctuations in the extracellular space (ECS) of in vitro preparations. Some of these issues will be carefully studied at different stages during postnatal development and correlated with important morphological or biochemical changes occurring at these times. A new research direction for this plan is the analysis of the single ion channel in cultured or isolated glial cells. Isolated rat optic nerves, tissue slices from rat neocortex, and cultured rodent astrocytes will be used in most experiments and offer several advantages over in vivo preparations including ready access of perfusion solutions to the ECS, direct visualization of microanatomic features of the tissue cells, and relative ease of intracellular recordings from neurons and glia. One component of the project will investigate characteristics of some of these issues in a non-mammalian preparation, the turtle brain. Using intracellular staining and recording techniques the following projects will be undertaken: 1) developmental study of glial cell physiology and morphology in the rat optic nerve; 2) electrophysiological, morphological, and metabolic studies on glia in the rat optic nerve; 3) mechanisms of slow potential generation and ECS ionic homeostasis in turtle cortex; 4) characterization of neural activity-dependent changes of pHo in rat optic nerve and neocortical tissue slice; 5) mechanisms of neural activity dependent ECS shrinkage; 6) patch clamp studies on single ionic channels of glia in vitro.